1. Field of the Invention
The present invention relates to a converging device, light source module, a laser device and an optical signal amplifier. More particularly, the present invention relates to a converging device for converging light having a high aspect ratio emitted from a semiconductor array laser to a small spot, and a light source module, a laser device and an optical signal amplifier using such converging device.
2. Description of the Related Art
In the field of optical communications, optical measurement and laser processing, a semiconductor array laser such as laser diode bar (hereinafter, referred to as LD bar) in which a plurality of laser diodes are horizontally aligned is used as a laser device or a pumping source for the laser device. A light emitting surface of the LD bar has a long horizontal axis of approximately 10 mm in a direction of alignment of the laser diodes and a short vertical axis of approximately 1 xcexcm in a thickness direction of the light emitting surface. Thus, a spot of the light emitted from such a light emitting surface has an elliptic shape having a high aspect ratio. When such a light is converged by a normal optical system, the light can be sufficiently converged in the vertical direction, however, the light can only be converged within at most, several millimeters in the horizontal direction.
Therefore, various devices have been developed for converging a light having a large aspect ratio emitted from the LD bar or the like to a small spot having substantially the same length in both directions. Such devices include a fiber coupling system, a two-mirror system and a triangle duct.
In the fiber coupling system, as shown in FIG. 40, the light is input to ends of a plurality of optical fibers 42 which are aligned horizontally adjacent the light emitting surface 40 of the LD bar. Other ends of the fibers 42 are bundled in a round shape to obtain round spot of light therefrom. In this system, however, as the light emitting surface of the converged light is formed by the end surfaces of the bundled fibers, a converging ratio is limited.
In the two-mirror system, as shown in FIGS. 41 and 42, the light is input between the two mirrors 50, 52 which are arranged in a parallel alignment from an upper diagonal upper direction to a lower diagonal direction. The mirrors 50, 52 have reflective surface 50a, 50b which face each other. The light input is reflected repeatedly between the reflective surface 50a, 52a so that the light is shifted both horizontally and vertically. The mirrors 50, 52 face toward each other and are horizontally and vertically space from each other. The light beam (1) passes above the mirror 52 to be emitted and the light beams (2)-(5) are reflected between the reflective surfaces 50a, 52a one to four times and output to be vertically beneath the light beam (1). The light beams (1)-(5) are converted from a horizontal alignment to a vertical alignment in the above manner. Thus, the spot of light is converged to 1/5 in horizontal direction. In this system, however, as a plurality of optical devices are used, alignment of the devices is complex, the cost and time for production and alignment is high and reliability of convergence is low.
In the triangle duct system, as shown in FIG. 43, a duct portion 12 having an equilateral triangle shape, which is made from a thin plate, is prepared. The light to be converged is input from an incident surface 12a, which is a surface at the base of the triangle extending in the thickness direction of the duct portion 12. The light is totally reflected in the reflective surfaces 12b, which is a surface at equal side extending in the thickness direction, to be transmitted toward a vertex of the triangle so as to be converged. The converged light is emitted to an optical fiber 27 provided at the vertex of the duct portion 12. According to the system, as the structure of the device is simple, the time and cost for production and alignment may be decreased, and the reliability for converging the light beams can be improved.
However, in the above triangle duct 12, as reflection of the light in the reflective surface 12b is repeated, an incident angle of the light in the reflective surface 12b decreases. As a result, when the light is intended to be converged to the smaller spot, the incident angle of the light in the reflective surface 12b cannot be maintained within a critical angle of a total reflection. Therefore, according to the above-configured duct, the maximum convergence of the light can only be in the range of 1/3-1/5.
FIG. 44 shows a result of a ray-tracing, in which four parallel light beams at 3 mm pitch are input in an equilateral triangle duct made of a silica glass having a thickness of 100 xcexcm, a vertical angle of 10xc2x0, and a width of the incident surface of 12 mm. The light introduced from the incident surface 12a is transmitted toward the vertex of the duct portion 12 by being reflected in the reflective surfaces 12b. As the reflection is repeated, the incident angle of the light in the reflective surface 12b decreases. Adjacent the vertex of the duct portion 12, the incidental angle of the light cannot be maintained within the critical angle of the total reflection and the light is leaked outside the duct portion 12. As a result, converged light with a small spot cannot be obtained from the vertex of the duct portion 12.
In order to solve the above problem, as shown in FIG. 45, a convex surface may be formed in the incident surface 12a of the duct portion 12 for refracting the light toward the vertex of the duct portion 12 in order to reduce the number of reflections in the reflective surface 12b. In such a duct, since both edges of the incident surface 12a cannot be placed closely to the light emitting surface of the LD bar 16, the light is leaked from both of the edges to lower a coupling efficiency.
Therefore, there is a demand for a converging device for converging the light to the smaller spot by utilizing the advantages of the triangle duct.
It is an object of the present invention to provide converging device which can efficiently converge a light having a high aspect ratio to a smaller spot with a simple structure. It is another object of the present invention to provide a light source module, a laser device and an optical signal amplifier using such a converging device.
In order to achieve the above object, there is provided a converging device comprising a converging portion for converging a light, said converging portion having an incident surface in which a light to be converged is introduced, a tip portion provided in an opposite side of said incident surface in a direction of transmission of said light and a reflective surface for reflecting said light introduced from said incident surface so that said light is transmitted toward said tip portion, and a guide portion provided in said reflective surface along a direction from said incident surface to said tip portion, wherein said light transmitted in said converging portion is introduced to said guide portion and said introduced light in said guide portion is reflected so that said light is transmitted toward one end of said guide portion in a tip portion side, said light transmitted in said guide portion toward said converging portion is transmitted by maintaining a condition of substantially total reflection with respect to said reflective surface of said converging portion, and said converged light is emitted from at least one of said tip portion and said one end of said guide portion.
In the above converging device, the light introduced to the converging device from the incident surface is transmitted toward the tip portion to be converged by being reflected in the reflective surface. The converged light is finally emitted from the tip portion or the end of the guide portion. According the above converging device, since the light transmitted in the converging portion is introduced to the guide portion, a length of the light path and the number of reflections of the light in the converging portion can be reduced. Thus, the light can be converged to a small spot before the incident angle of the light in the reflective surface becomes smaller than the critical angle of the total reflection.
In the above converging device, said converging portion is formed in a shape of a triangle and made of a thin plate which is optically transparent with respect to a wavelength of light to be converged. The incident surface is a surface at one side of said triangle extending in a thickness direction of the converging portion, said reflective surface is a surface at other side of said triangle which extends in a thickness direction of said converging portion, and said tip portion is a vertex of said triangle spaced from said incident surface.
In the above converging device, the converging portion is made in a shape of a triangle plate. The light is introduced from the incident surface which is a face at one side of the triangle extending in a thickness direction of the converging portion. The light is transmitted toward the tip portion of the triangle to be converged by being reflected between the reflective surfaces which are surfaces at other sides of the triangle extending in a thickness direction of the converging portion. When light reaches a boundary between the converging portion and the guide portion, the light is introduced in the guide portion and transmitted therein. The converged light is finally emitted from the tip portion or the end of the guide portion.
According the above converging device, when the light reaches a boundary between the converging portion and the guide portion, the light is introduced in the guide portion and transmitted therein. Thus, a length of the light path and the number of reflections of the light in the converging portion can be reduced. As a result, the light can be converged to a small spot before the incident angle of the light in the reflective surface becomes smaller than the critical angle of the total reflection.
In the above converging device, the guide portion can be provided along from said incident surface to said tip portion. According to the above invention, the guide portion can be easily produced and the light is easily introduced from the converging portion and the guide portion.
In the above converging device, the guide portion can be formed in a shape of a fiber. According to the above converging device, the converged light can be output from the guide portion.
In the above converging device, said guide portion may have a free curved surface formed by melting said reflective surface of said converging portion. According to the above converging device, the guide portion with a smooth surface can be prepared by a simple operation.
In the above converging device, said converging portion may have a shape of a thin plate, and a maximum thickness of said guide portion in a thickness direction of said converging portion is more than two times that of said converging portion. In the above converging device, when the guide portion has a circular cross-section, the maximum thickness means a diameter of the guide portion. According to the above converging device, the light can be easily confined in the guide portion and the light can be transmitted longer in the guide portion. Thus, the
In the above converging device, said converging portion has a shape of a thin plate and a gap is formed between the center of said converging portion and that of said guide portion. According to the present converging device, an incident angle of the light introduced from the converging portion to the guide portion can be made larger. Thus, since the light can be easily confined in the guide portion, the light can be converged to a small spot.
The above object of the present invention is achieved by a light source module comprising a light source having a light emitting surface for emitting a light, said light emitting surface having a short axis and a long axis, and a converging device for converging said light, said converging device comprising a converging portion for converging a light, said converging portion having an incident surface in which said light to be converged is introduced, a tip portion provided in an opposite side of said incident surface in a direction of transmission of said light and a reflective surface for reflecting said light introduced from said incident surface so that said light is transmitted toward said tip portion, and a guide portion provided in said reflective surface along a direction from said incident surface to said tip portion, wherein said light transmitted in said converging portion is introduced to said guide portion and said introduced light in said guide portion is reflected so that said light is transmitted toward one end of said guide portion in a tip portion side, said light transmitted in said guide portion toward said converging portion is transmitted by maintaining a condition of substantially total reflection with respect to said reflective surface of said converging portion, and said converged light is emitted from at least one of said tip portion and said one end of said guide portion. According to the present light source module, a light having a high aspect ratio which is emitted by a LD bar or the like can be converged to a small spot.
The above object of the present invention is achieved by a light source module comprising a light source having a light emitting surface for emitting a light, said light emitting surface having a short axis and a long axis, and a plurality of converging devices for converging said light, said converging device is aligned in one of a horizontal direction and a vertical direction, each of said converging device comprising a converging portion for converging said light, said converging portion having an incident surface in which a light to be converged is introduced, a tip portion provided in an opposite side of said incident surface in a direction of transmission of said light and a reflective surface for reflecting said light introduced from said incident surface so that said light is transmitted toward said tip portion, and a guide portion provided in said reflective surface along a direction from said incident surface to said tip portion, wherein said light transmitted in said converging portion is introduced to said guide portion and said introduced light in said guide portion is reflected so that said light is transmitted toward one end of said guide portion in a tip portion side, said light transmitted in said guide portion toward said converging portion is transmitted by maintaining a condition of substantially total reflection with respect to said reflective surface of said converging portion, and said converged light is emitted from at least one of said tip portion and said one end of said guide portion.
According to the present light source module, since a light emitted from one light source is converged by a plurality of converging devices, the light can be converged in a smaller spot. In this light source module, a plurality of converging devices can be arranged both horizontally and vertically, in another words, in second dimension.
The above object of the present invention is achieved by a laser device comprising a laser fiber including a laser medium, said laser fiber outputting a laser beam when said laser medium is pumped, a light source for emitting a pumping light to pump said laser medium, a converging device for converging said pumping light, said converging device comprising a converging portion for converging said pumping light, said converging portion having an incident surface in which said pumping light to be converged is introduced, a tip portion provided in an opposite side of said incident surface in a direction of transmission of said pumping light and a reflective surface for reflecting said pumping light introduced from said incident surface so that said pumping light is transmitted toward said tip portion, and a guide portion provided in said reflective surface along a direction from said incident surface to said tip portion, wherein said pumping light transmitted in said converging portion is introduced to said guide portion and said introduced pumping light in said guide portion is reflected so that said pumping light is transmitted toward one end of said guide portion in a tip portion side, said pumping light transmitted in said guide portion toward said converging portion is transmitted by maintaining a condition of substantially total reflection with respect to said reflective surface of said converging portion, and said converged pumping light is emitted from at least one of said tip portion and said one end of said guide portion, an optical member made of an optically transparent material with respect to said pumping light, in which said pumping light converged by said converging device is confined, and wherein at least a part of a lateral side of said laser fiber is connected to said optical member either directly or via an optical medium and said laser medium is pumped by said pumping light transmitted from said optical member to said laser fiber.
In the above laser device, the pumping light emitted from the light source is converged by the converging device and the converged pumping light is confined in the optical member. When the pumping light reaches a boundary between the optical member and the laser fiber, the pumping light is introduced in the laser fiber. The pumping light stimulates the laser medium doped in the core to generate a laser beam by a stimulated emission effect. The laser beam travels in the laser fiber to be output from the end.
According to the above laser device, the laser beam is generated by the pumping light with a high energy density, which is converged by the converging device. Therefore, a desired amount of the pumping light can be introduced in the optical member, depending upon target laser power, a high power laser beam can be provided. In addition, since the pumping light can be introduced to the optical member from a small area of the optical member, radiation of the pumping light can be limited.
The above object of the present invention is achieved by a laser device comprising a pumping source for emitting a pumping light, and a converging device for converging said pumping light, said converging device comprising a converging portion for converging said pumping light, said converging portion having an incident surface in which said pumping light to be converged is introduced, a tip portion provided in an opposite side of said incident surface in a direction of transmission of said pumping light and a reflective surface for reflecting said pumping light introduced from said incident surface so that said pumping light is transmitted toward said tip portion, and a guide portion provided in said reflective surface along a direction from said incident surface to said tip portion, wherein said pumping light transmitted in said converging portion is introduced to said guide portion and said introduced pumping light in said guide portion is reflected so that said pumping light is transmitted toward one end of said guide portion in a tip portion side, said pumping light transmitted in said guide portion toward said converging portion is transmitted by maintaining a condition of substantially total reflection with respect to said reflective surface of said converging portion, wherein said guide portion is a laser fiber including a laser medium, said guide portion outputting a laser beam when said laser medium is pumped by said pumping portion.
In the above laser device, the pumping light emitted from the light source is introduced in the converging device. The pumping light is transmitted toward the tip portion of the converging portion by being reflected in the reflective surface of the converging portion. The pumping light is introduced in the laser fiber. The pumping light stimulates the laser medium doped in the core to generate a laser beam by a stimulated emission effect. The laser beam travels in the laser fiber to be output from the end.
According to the above laser device, the laser beam is generated by the pumping light with a high energy density, which is converged by the converging device. Therefore, a desired amount of the pumping light can be introduced in the optical member, depending upon target laser power, a high power laser beam can be provided. In addition, since the pumping light can be introduced to the optical member from a small area of the optical member, radiation of the pumping light can be limited.
The above object of the present invention is achieved by an optical signal amplifier for amplifying an optical signal comprising a laser device, said laser device comprising a laser fiber including a laser medium, said laser fiber outputting a laser beam when said laser medium is pumped, a light source for emitting a pumping light to pump said laser medium, a converging device for converging said pumping light, said converging device comprising a converging portion for converging a light, said converging portion having an incident surface in which a pumping light to be converged is introduced, a tip portion provided in an opposite side of said incident surface in a direction of transmission of said pumping light and a reflective surface for reflecting said pumping light introduced from said incident surface so that said pumping light is transmitted toward said tip portion, and a guide portion provided in said reflective surface along a direction from said incident surface to said tip portion, wherein said pumping light transmitted in said converging portion is introduced to said guide portion and said introduced light in said guide portion is reflected so that said pumping light is transmitted toward one end of said guide portion in a tip portion side, said pumping light transmitted in said guide portion toward said converging portion is transmitted by maintaining a condition of substantially total reflection with respect to said reflective surface of said converging portion, and said converged light is emitted from at least one of said tip portion and said one end of said guide portion, a optical member made of an optically transparent material with respect to said pumping light, in which said pumping light converged by said converging device is confined, and wherein at least a part of a lateral side of said laser fiber is connected to said optical member either directly or via an optical medium and said laser medium is pumped by said pumping light transmitted from said optical member to said laser fiber, wherein one end of said laser fiber is an input end of said optical signal and the other end is an output end of said optical signal.
The above object of the present invention is achieved by a optical signal amplifier for amplifying an optical signal comprising a laser device, said laser device comprising a pumping source for emitting a pumping light, and a converging device for converging said pumping light, said converging device comprising a converging portion for converging said pumping light, said converging portion having an incident surface in which said pumping light to be converged is introduced, a tip portion provided in an opposite side of said incident surface in a direction of transmission of said pumping light and a reflective surface for reflecting said pumping light introduced from said incident surface so that said pumping light is transmitted toward said tip portion, and a guide portion provided in said reflective surface along a direction from said incident surface to said tip portion, wherein said pumping light transmitted in said converging portion is introduced to said guide portion and said introduced pumping light in said guide portion is reflected so that said pumping light is transmitted toward one end of said guide portion in a tip portion side, said pumping light transmitted in said guide portion toward said converging portion is transmitted by maintaining a condition of substantially total reflection with respect to said reflective surface of said converging portion, wherein said guide portion is a laser fiber including a laser medium, said guide portion outputting a laser beam when said laser medium is pumped by said pumping portion, wherein one end of said laser fiber is an input end of said optical signal and the other end is an output end of said optical signal.
According to the above inventions, optical signal amplifiers can be realized by utilizing the laser device with a high efficiency.